1. Field of the Invention
The present invention relates to an ink supply system utilized for an ink jet recording apparatus or the like, and also, an ink jet recording apparatus. More particularly, the invention relates to an ink supply system a part of ink container of which is replaceable, and to an ink jet recording apparatus as well.
2. Related Background Art
An ink jet recording apparatus is the one that records by discharge ink from recording means (an ink jet head) to a recording medium, which has been widely used in recent years owing to the advantages, among some others, that the recording means can be made compactly with ease; the amount of noises is smaller with the adoption of non-impact method; and color images can be made easily with the capability to use various kinds of ink in many ways.
As the ink supply system used for the ink jet recording apparatus, there has conventionally been known the one which is detachably mounted on a carriage that carries an ink jet head, and an ink tank connected and communicated with the ink jet head. Here, an ink absorbent having ink absorbed and retained in it in advance is filled in the ink tank, thus making it possible to supply ink retained in the ink absorbent to the ink jet head. For an ink supply system of the kind, it is generally practiced to arrange the structure so that an ink absorbent formed by a porous substance, such as polyurethane form, is filled in the housing of an ink tank, and then, a tank cover is welded to it. With the structure thus arranged, there is an advantage that ink is retained stably in the ink tank irrespective of movement or vibration given to it.
However, along with the higher speeds required for an ink jet recording apparatus in recent years, it becomes necessary to supply ink to the head in a larger amount at a shorter period of time. As a result, the amount of ink to be used becomes more increasingly, while the ink supply system described above has the ink absorbent filled almost entirely in the interior of the ink tank. Therefore, the amount of retainable ink is naturally limited only to the capacity of the absorbent that may be contained in the tank. The resultant amount of ink that can be injected becomes considerably smaller against the volume of the ink tank as compared with the ink supply system which is structured to allow ink to be injected up to an amount almost equally to the total volume of an ink tank having no ink absorbent in it.
Also, the capillary member, such as porous substance, tends to increase the flow resistance along the supply amount of ink. In addition, the flow resistance changes depending on the printing duty. As a result, the negative pressure exerted on the head orifices is caused to change greatly. Then, there is a fear that this makes the fluctuation of discharge amount greater. Also, the higher quality of images and the multiple use of ink are more in demand so that a slight change of ink composition may influence the finish of recorded images inevitably. In other words, the capillary member, such as porous substance, has a large surface area (liquid contact area with ink), and it is required for this member to provide a rigid chemical stability so that no decomposition nor elution should occur when it is in contact with ink. Thus, the selection of material usable as porous substance is automatically limited in consideration of reactive binding, physical adsorption, or the like.
With a view to solving the problems discussed above, the present invention is designed. It is an object of the invention to provide an ink supply system which comprises an ink jet head for discharging ink; and a negative pressure generating container provided for a passage capable of distributing ink, including an ink tank retaining ink to be supplied to the ink jet head, and generating negative pressure by means of restoring force at the time of being deformed.
In accordance with the present invention, it is possible to perform stable recording, because the fluctuation of flow resistance due to the fluctuation of discharge amount is made smaller, and also, there is almost no fluctuation of pressure along the carriage operation. Therefore, the retaining amount of ink becomes suitably greater for the performance of higher speed printing. Moreover, the replacement of ink tanks is possible, while ink still remains in the negative pressure container, hence making it possible to prevent the complete ink shortage essentially. Also, with the smaller liquid contact area of the member that should be in contact with ink, the range of material selection becomes wider for such member.
Here, the ink jet head may be arranged for one end portion of the passage capable of distributing ink. Also, it may be possible to arrange the ink tank for the other end portion of the passage capable of distributing ink, and to enable the negative pressure generating container to lie between the ink jet head and the ink tank.
Or, it may be possible to arrange the negative pressure generating container for the other end portion of the passage capable of distributing ink, and between the ink jet head and the ink tank. In this case, it becomes possible to allow the negative pressure generating container which is positioned on the other end portion to function as a buffer tank, thus absorbing the fluctuation of pressure due to changes of the atmospheric pressure or temperature in order to suppress the influence that may be exerted on ink discharges.
Also, the negative pressure generating container may be a container formed by multiple layers, and provided with outer layer forming a housing of substantially polyhedral column shape, and an inner bag arranged inside the outer layer correspondingly, being capable of retaining ink therein and elastically deformable along the lead-out of ink.
Here, the inner bag may be provided with an air escape port on the upper part thereof, and the inner bag may be formed by material having low gas permeability.
The negative pressure generating container may be a container formed by multiple layers, and the outermost layer is a housing of substantially polyhedral column shape, and the innermost layer is an elastically deformable inner bag formed by material having high gas permeability, and ink can be retained in a space between the housing and the inner bag.
The negative pressure generating container may be a container formed by multiple layers, and the outermost layer is a substantially tubular shape, and the innermost layer is structured to provide inner walls being capable of distributing ink and elastically deformable along the lead-out of the ink, and one or more of the containers are continuously connected. In this case, it becomes possible to make an ink jet recording apparatus smaller as a whole.
The negative pressure generating container may be a container formed by multiple layers, and the outermost layer is a housing of substantially polyhedral column shape, and the innermost layer is in either one of modes of having an inner bag being capable of distributing ink and elastically deformable along the lead-out of the; having an ink containing chamber for retaining ink, and a buffer chamber separated from the ink containing chamber by a partition wall, but communicated therewith through a communicating portion; and having an ink containing bag in a housing. In this case, the effect is made higher on the ink leakage. Also, since the ink tank is provided itself with the function to generate negative pressure, there is no restriction imposed upon the position of the ink tank to make miniaturization possible for an ink jet recording apparatus, as well as to enhance the freedom of planning and designing thereof. Also, by means of multiple layer blow molding or the like, manufacture becomes possible with one molding process simply at lower costs.
Also, with the ink tank, there may be further connected a buffer container structured with multiple layers, having the outermost layer thereof being a housing of substantially polyhedral column shape, and the innermost layer being inner walls elastically deformable by the environmental changes.
The negative pressure generating container may be gas-liquid separation means capable of transmitting to the outside the gas existing in ink retained in a container. Then, the gas-liquid separation means may comprise an inner bag having high gas permeability for constituting the negative pressure generating container, and pressure reduction means connected with the negative pressure generating container.
A space may be provided for the interface between the housing and inner bag to constitute the negative pressure generating container, and pressure generating means is connected with the space.
The pressure generating means may be means for reducing pressure against the atmospheric pressure.
The inner bag may be formed by material having high gas permeability.
The pressure generating means may be means for applying pressure to the atmospheric pressure.
The ink jet recording apparatus of the present invention is provided with an ink supply system having either one of the structures described above.